Vasodilators Vasodilators

These drugs act primarily on the peripheral vasculature and reduce the workload on the heart. Some vasodilators, e.g. nitrates, cause venodilation, reducing venous return to the heart, and thereby decreasing systemic and pulmonary venous pressures (preload). Others, e.g. hydralazine, cause arteriodilation thus reducing afterload on the left ventricle. Some vasodilators, e.g. prazosin, nitroprusside and the angiotensin-converting enzyme (ACE) inhibitors (e.g. enalapril and captopril) have effects on preload and afterload.

Conventional vasodilators such as hydralazine and isosorbide dinitrate stimulate the sympathetic system and the renin-angiotensin-aldosteron-ADH system resulting in sodium and water retention, which may be detrimental to some patients. Therefore they are probably best used in combination with cardiac glycosides and diuretics.

Concurrent treatment with ACE inhibitors (e.g. enalapril) offers a good therapeutic approach to clinical cases not responding to diuretics and digoxin therapy alone. Marked hypotension can be a problem following the initial oral dose of an ACE inhibitor particularly in patients on diuretics or on a low salt diet, and patients are best hospitalised during the introduction of ACE inhibitors. Any drug that induces hypotension may precipitate prerenal azotaemia and acute renal failure in at-risk patients, and ACE inhibitors are contraindicated in the presence of renal impairment. In old animals renal function should be monitored closely before, and for at least a week after the use of these drugs, and diuretic doses should be reduced when they are administered at the same time.



Enalapril maleate


Glyceryl trinitrate

Prazosin hydrochloride

Sodium nitroprusside